This invention relates to apparatus employed in melt spinning of metals and metallic alloys to produce polycrystalline or amorphous foil. More particularly, it is concerned with an apparatus useful in the production of wide continuous foil by the double roller chill quenching method.
Melt spinning of metals is a process whereby a free jet of molten metal is impinged upon a rapidly moving cooled surface to chill quench the molten material to produce continuous foil. Melt spinning of metallic alloys provides the advantage that the rapid temperature quenching of the molten material, often on the order of 10.sup.3 to 10.sup.6 deg C. sec.sup.-1, permits the production of solid solutions of two or more metals which are mutually insoluble in the solid state and would otherwise separate upon slow cooling.
Numerous methods have been proposed for the melt spinning of metallic alloys including the double roller technique described by H. S. Chen et al. in Rev. Sci. Instrum., 41:1237 (1970) and by E. Babic et al. in J. Phys. (Section E) Sci. Instrum., 3:1014 (1970). In general, their apparatus comprised two rollers arranged with their axes parallel and driven to contrarotate at about 100-5000 rpm. Molten metal was delivered to the gap between the rollers where it was quenched by contact with the cool roller surfaces to produce thin foil.
However, in following the twin roller quenching technique, it is necessary that the metal be completely quenched to the solid state before it reaches the point of minimum gap spacing between the rollers since there is no contact between the metal and the roller surfaces after this point to provide further conductive cooling. Puddling of excess molten metal on the rollers, coupled with complete quenching of the metal to the solid state before it reaches the point of minimum spacing between the rollers results in the production of foil which is thicker than the roller gap spacing. This phenomenon causes serious problems in double roller apparatus where the roller positions are fixed, and virtually eliminates the possibility of producing continuous metal foil, that is, foil strips of lengths greater than a few meters.
In those instances where the high temperature fracture toughness of the resulting foil is less than the pressure exerted by fixed rollers, when excess metal is forced between the rollers, the foil will have cracks and slippage plane deformations which render it unusable for most applications. Moreover, the bumping and bouncing of the rollers which results in such situations causes the foil to have non-uniform thickness and width.
On the other hand, if the high temperature fracture toughness of the foil is greater than the pressure exerted by the fixed rollers, when excess metal is forced between the rollers, it scores or otherwise damages the surfaces of the rollers. This becomes a particular problem when the rollers are faced with copper or other soft metal, chosen because of its superior heat conductive property.
One apparatus designed with a view to overcoming the problems discussed above is disclosed in U.S. Pat. No. 3,881,541. In the apparatus disclosed therein, the rollers are narrow and are coextensive with the desired width of the foil filament, about 0.003 inch to 0.100 inch. Excess molten metal delivered to the roller gap displaces laterally along the roller faces where it is removed at the roller edges as unwanted flash by means of an air knife. The resulting foil is of a thickness equal to the fixed roller gap spacing and width equal to the roller face width.